I fall into most of those already listed.
#1 [by far]: Evil Humanoids, in general. Kobolds, goblins, orcs, hobgoblins, ogres, bugbears a bit less so, evilly-disposed lizardmen, troglodytes, etc... Generally speaking, evil humanoids are always the mooks/minions of evil, found everywhere in seeming unending numbers.
#2: I have noticed a pension, particularly at lower levels (where a great deal of my games occur), of overusing faye beings. Dryads, pixies, nixies, redcaps, leprechauns, etc... Generally speaking, these are not antagonistic encounters, often even being helpful influences for the party. But they do "show up" quite a lot in my games. In all fairness, satyrs and sprites might make such regular appearance because they exist as a PC race in my campaign world.
#3: Undead. Easy peasy, no moral ambiguity. It's undead. It's evil. I use skeletons, zombies, shadows, and, particularly, ghouls vastly more often than "free-willed" undead, so there isn't even any moral/ethical question of it as a 'thinking" creature. Nothing makes for completely guilt-free hack'n'slash like hordes of undead.
#4: Someone mentioned stirges...yeah...I use stirges a lot. But, let's be real...you can never have too many stirges. boowa. ha. ha.

#5: mmm...this is a toss up between Demons/demonic creatures or Dragons/draconic creatures. Not really sure which I use more of, but both (moreso the type-of-creature than full-on demons or dragons) make an, I'd say, "above average" amount of use in many/most games/plots/campaigns.
There's my top 5.